Strange Problem connecting to a wifi subnet

hi, I have problems connecting to a wifi subnet. The chain of connections is made up as follows: a TIM Fibra modem router with wifi whose address is Then there is an alpha AWUS0036NH USB dongle connected to the second ZBT open wrt router with address and the PC with address It is a single internet connection shared between the ground floor apartment and the second floor. Well, opening the web screen of the ZBT router I see that the wifi of the ZBT router sees the wifi network of the TIM modem router with all its parameters
(signal percentage at 61%, the SSID, the Client mode, the MAC, etc., however, in the Associated Station list under the IPv4 Address entry, instead, it marks me "?" (a question mark) i.e. the ZBT router has not assigned it a IP address of the class
Instead, it usually assigns it the address The ZBT router has set the DHCP automatically, while in the main TIM modem router in a special menu I have assigned the device with this address with the relative SSID name of the ZBT router. This failed connection occurs the moment I turn off the ZBT router. But if I keep it on for days, nothing happens. It must be said that there are usually about 6-8 devices connected to the wifi network of the TIM modem router, including the ZBT wlan router. Unfortunately the TIM modem router does not have specific functions to make the connection of the ZBT wlan router more preferential, but I would like to know what happens?
Sometimes I reboot the ZBT router and it manages to connect, sometimes I can only do it by upgrading the settings backup file, sometimes I just can't even though the ZBT router sees the network and I try both with the reboot the router or back up the last settings file.
I would like to know what happens: maybe when I exit the connection on the next attempt I don't connect because there are too many connections?
Sometimes it happens that it doesn't connect even for 2 days; then suddenly it reconnects.
Is it possible to solve the problem? I was told to set the preferential address of the ZBT WLAN router in the TIM modem router, but the latter does not have these functions because it is a very basic modem router. Thanks for the info

This is pretty hard to understand... maybe a network diagram would help.

Also, what device(s) is configured with OpenWrt?